In recent years, in view of energy saving and preservation of environment, an optical semiconductor device light source has begun to be installed as a light source for illumination in tail lamps etc. of vehicles.
The optical semiconductor device light source comprises an optical semiconductor device chip, a package that embeds the chip and has light-reflecting properties, an epoxy resin sealant body containing fluorescent material, and an optical lens that is made of transparent resin and covers these aforementioned components.
The optical lens is an optical part that emits light, working as a point light source, by collecting the light emitted from the optical semiconductor device chip and transformed in a layer containing fluorescent material.
It is desirable that the lens of optical semiconductor device mounted on vehicles is made of a material having environment resistance against steam, high temperature aging, etc. and a transparent resin is required, which has high resistance against heat and steam and excellent processability for molding.
As a resin having high heat resistance and high optical transparency a cyclic olefin resin is listed.
While the cyclic olefin resin has a total light transmission as high as 91 to 93% and has an excellent transparency, it has a drawback of limited usage environment since it has poor resistance against high temperature aging.
For example, when a lens of optical semiconductor device mounted on vehicles, which is made of cyclic olefin resin, is used for a backlight illumination device such as a headlight, an instrument panel, a taillight, a winker etc., the lens product shows yellowing in a high-temperature aging-resistance test environment at temperatures of 110 to 140° C. or more, so that cyclic olefin resin cannot be used.
On the other hand, polycarbonate type resin has an excellent resistance in the high-temperature aging-resistance test environment, but its resistance against hydrolysis decreases due to the effect of impurities, antioxidants and the like, so that in automobile use polycarbonate type resin still has a problem of heavy clouding in a pressure cooker test under a saturated steam pressure (for 100 hours at 120 to 127° C.), which is required in a particularly severe exterior use.
In order to solve the problem, compositions prepared by blending special arylphosphine, phosphines and oxetane compounds and/or epoxide compounds with polycarbonate type resin have been proposed, for example in the following referenced patent documents 1 and 2.
However, these polycarbonate type resin compositions still do not have sufficient optical properties.
Referenced patent document 1: Japanese published unexamined application No. H8(1996)-231840.
Referenced patent document 2: Japanese published unexamined application No. H9(1997)-227863.